GCDAsyncUdpSocket Multicast Gets HTTP 412 Response - objective-c

Question

I am building a iOS application that sends out a multicast message (SSDP) and listens for responses from devices that implement that protocol. I am using GCDAsyncUdpSocket to create the UDP socket to broadcast the SSDP message and receive responses. The problem that I am having is that the message the application receives from the all of the devices on the network is the same: a HTTP 412 response.
Here is my code:
Initialize socket
#interface ViewController ()
{
GCDAsyncUdpSocket *udpSocket;
}
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_main_queue()];
NSError *error = nil;
if (![udpSocket bindToPort:0 error:&error])
{
NSLog(#"Error binding: %#", [error description]);
return;
}
if (![udpSocket beginReceiving:&error])
{
NSLog(#"Error receiving: %#", [error description]);
return;
}
[udpSocket enableBroadcast:YES error:&error];
if (error != nil)
{
NSLog(#"Error enableing broadcast: %#", [error description]);
return;
}
NSLog(#"Socket Created");
}
Create Socket
- (IBAction)socketFind:(id)sender
{
NSString *str = [[NSString alloc] initWithString:#"M-SEARCH * HTTP/1.1\r\nHOST: 239.255.255.250:1900\r\nMAN: \"ssdp discover\"\r\nMX: 3\r\nST: ssdp:all\r\nUSER-AGENT: iOS UPnP/1.1 TestApp/1.0\r\n\r\n"];
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
[udpSocket sendData:data toHost:#"239.255.255.250" port:1900 withTimeout:-1 tag:0];
NSLog(#"Sent Data");
}
Data Received Callback
- (void)udpSocket:(GCDAsyncUdpSocket *)sock didReceiveData:(NSData *)data
fromAddress:(NSData *)address
withFilterContext:(id)filterContext
{
NSLog(#"Did Receive Data");
NSString *msg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
if (msg)
{
NSLog(#"Message: %#",msg);
}
else
{
NSString *host = nil;
uint16_t port = 0;
[GCDAsyncUdpSocket getHost:&host port:&port fromAddress:address];
NSLog(#"Unknown Message: %#:%hu", host, port);
}
}
When the didReceiveData function is called, I get the following message:
Message: HTTP/1.1 412 Precondition Failed
Connection:close
CONTENT-LENGTH:0

Answer 1

This issue was with the M-Search string. I was missing the colon between sspd and discover. If you are getting a 412 response, I would make sure that you are formatting everything correctly. Turns out, that was my issue...